This invention relates to electronic shifters for bicycles and, more particularly, to an electronic shifter using relative index shifting.
It is known in the art relating to bicycles to provide electronic shifters to actuate a gear shifter to shift a gear mechanism between gears. The system usually includes a controller or microprocessor for generating a shift signal in response to the rider manually selecting a upshift or downshift. The method of shifting may be based on absolute index shifting or relative index shifting. With absolute indexing, the shifting system has a predetermined number of gears which corresponds to an equivalent number of shift inputs that the user depresses in order to select a gear. A simple form of the electronic absolute shifter has a specific shift input button for each gear. A problem associated with such a configuration is that when one of the shift input button does not match the corresponding gear, the system does not function properly. To prevent this type of malfunction, a more complex electronic system is needed. This system requires several additional components such as a device for determining the current gear; additional computer programming to prevent miscommunication between the shift input and the actual gear; and a more costly sophisticated microprocessor to coordinate such tasks. A robust absolute shifting system requires additional complexity and costs.
In a relative indexing shifting system, each gear does not need a specific shift input rather each input represents only a generic shift. Each time the shift input is depressed the system shifts relative to the current gear. The command is not, xe2x80x9c1 to 3 . . . 3 to 5 . . . 5 to etc., but rather a more simple command, xe2x80x9cup . . . up . . . or down . . . down . . . , etc.xe2x80x9d This type of relative index shifting has several disadvantages. For instance, the electronic shifter may include two shift buttons, one for upshifting and the other for downshifting. This type of shifter requires the rider too rapidly push the buttons to perform multiple shifts. Another type of relative shifter is a return-to-center shifter wherein the shifter has three positions, a center, a forward twist and a reward twist. The rider twists the shifter forward or backward to shift and then the shifter returns to center under spring load. The disadvantage with this configuration is that the rider must perform twist-release, twist-release motions to perform multiple shifts. Therefore, there is a need to provide an electronic shifter that uses the simplicity of relative shifting and provides an ergonomic configuration that allows the rider to perform multiple shifts with a single movement.
The present invention provides an electronic shifter for shifting a bicycle gear mechanism between a plurality of gears. The shifter includes a stationary member mountable to a handlebar of the bicycle and a rotating member rotatable with respect to the stationary member to define predetermined positions of the members with respect to each other. The predetermined positions correspond to the plurality of gears. An electrical switch is operatively connected the rotating member for generating a shift signal in response to the rotating member rotating from one predetermined position to another predetermined position.
In one embodiment of the present invention, the rotating member may rotate about an axis perpendicular to the handlebar. Alternatively, the rotating member may rotate about an axis coaxial of the handlebar. The stationary member includes a first plurality of detents disposed on a surface of the stationary member. The rotating member includes a second plurality of detents disposed on a surface of the rotating member. The second plurality of detents are engagable with the first plurality of detents. The configuration of the first and second plurality of detents is such that upon rotation of the rotating member the first and second plurality of detents disengage to allow rotation of the rotating member. A resilient member biases the second plurality of detents to engage with the first plurality of detents. Rotation of the rotating member in a first direction causes the gear mechanism to be shifted in an upshift direction and a rotation of the rotating member in a second direction causes the gear mechanism to shift in an downshift direction.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention take together with the accompanying drawings.